The communications and radar industries have interest in reactive-type broadband high-power microwave dividers and combiners. Even though not all ports are RF matched, as compared to the Wilkinson power divider/combiner (see Ernest J. Wilkinson, “An N-way hybrid power divider,” IRE Trans. on Microwave Theory and Techniques, January, 1960, pp. 116-118), the reactive-type mechanical and electrical ruggedness is an advantage for high-power combiner applications. This assumes that the sources to be combined are isolator-protected and of equal amplitude and phase.
An example of prior art, commercially available 6-way reactive power divider (Model D6-85FE by Microlab/FXR) is shown in FIGS. 1 and 2. Microwave power into a 50 ohm coax input port 101 enters a coaxial stepped impedance transformer 102 followed by a 6-way divider port structure 104. Equally-divided power exits the six 50 ohm output connectors 103. The coaxial impedance transformer 102 is designed to minimize reflected power over a desired passband frequency range f1 to f2. FIG. 3 shows a generalized equivalent electrical circuit for this type of reactive power divider. A simple stepped-impedance transformer is typically used, shown in FIG. 3 as transformer sections having characteristic impedances Z1 through ZT with respective phase lengths θ1 through θT—usually each a quarter-wavelength at the mid-band frequency within the passband. The input port 101 (FIGS. 1, 2) impedance is ZS, and each output port 103 impedance is ZL. The quantity N output ports are connected in parallel at a common junction, so that the circuit load impedance is ZL/N (FIG. 3). Values for the transformer characteristic impedances Z1 through ZT are dependent on the desired voltage standing wave ratio (VSWR) over the frequency range f1 to f2, as well as the source and load impedance quantities ZS and ZL/N. For broadband applications, this type of reactive power divider is physically quite long, because of the limitation of using a simple quarter-wave stepped impedance transformer between a 50 ohm source impedance and a 50/N ohm load impedance.
Another prior art reactive combiner/divider example is U.S. Pat. No. 8,508,313 to Aster, incorporated herein by reference. Broadband operation is achieved using two or more stages of multiconductor transmission line (MTL) power divider modules. An 8-way reactive power divider/combiner 200 of this type is shown in FIGS. 4 and 5. Described as a power divider, microwave input power enters coax port 201, which feeds a two-way MTL divider 202. Input power on the main center conductor 206 (FIG. 6a, Section a1-a1) is equally divided onto two satellite conductors 207 which in turn each feed quarter-wave transmission lines housed in module 203 (FIG. 4). Each of these quarter-wave lines feeds a center conductor 208 (FIG. 6b, Section a2-a2) in its respective four-way MTL divider module 204, power being equally divided onto satellite conductors 209 which in turn feed output coax connectors 205. This may also be described as a two-stage MTL power divider where the first stage two-way divider (Stage B, FIG. 7) feeds a second stage (Stage A, FIG. 7) consisting of two 4-way MTL power dividers, for a total of eight outputs 205 of equally divided power. This two-stage divider network is described electrically in FIG. 7 as a shorted shunt stub ladder filter circuit with a source admittance YS(B) and a load admittance NS(B)NS(A)YL(A). The first-stage (Stage B) quarter-wave shorted shunt stub transmission line characteristic admittances have values Y10(B) and NS(B)Y20(B), respectively, which are separated by a quarter-wave main line with characteristic admittance value NS(B)Y12(B). Here the number of satellite conductors NS(B)=2, NS(A)=4 and Y12(B) is the value of the row 1, column 2 element of the 3×3 characteristic admittance matrix Y(B) for the two-way MTL divider (Section a1-a1, FIG. 6). Also, Y10(B)=Y11(B)+NS(B)Y12(B) and Y20(B)=Y22(B)+Y12(B)+Y23(B). Each quarter-wave transmission line within housing 203 (FIG. 4) has characteristic admittance YT and is represented in the equivalent circuit FIG. 7 as a quarter-wave main transmission line with characteristic admittance NS(B)YT. The second stage (Stage A) quarter-wave shorted shunt stub transmission line characteristic admittances have values NS(B)Y10(A) and NS(B)NS(A)Y20(A), respectively, which are separated by a quarter-wave main line with characteristic admittance NS(B)NS(A)Y12(A). Here Y12(A) is the value of the row 1, column 2 element of the 5×5 characteristic admittance matrix Y(A) for one of the two identical four-way MTL divider modules 204 (FIG. 4) with cross-section a2-a2 in FIG. 6b. A plot of scattering parameters for an octave bandwidth two-stage eight-way divider is shown in FIG. 4c of U.S. Pat. No. 8,508,313. Due to its complexity, the two-stage, three MTL module power divider/combiner as shown in FIGS. 4 and 5 is expensive to fabricate.